Transmission shakes when I hammer it. AOD-E...help

I recentlly took it to a mechanic, because I was having problems with a leak in my tranmission. Anyways, they said a couple of bolts where loose (I don't think they where pan bolts) and that's why my transmission was leaking oil, so they tighted those bolts.

Now I noticed shaking under the car (not the wheel, but my dash, stereo, etc) while I was racing tonight. Like I said, when I hammer it around 4K, or 5K rpms it starts shaking. This has happened on more than one ocassion just tonight.

Should I be worried ? I also checked for any leaks (tranny), and found none.

I'd rather mod the engine, thean buy a new tranny, so that's why I came here.